There is a projection type display device, such as a liquid crystal projector, which changes light from a light source, such as an electric bulb, to a contrast per pixel image using a light valve device, such as a liquid crystal panel, and projects an enlarged image on a screen or the like. Further, as the light valve device of the display device, devices of two operation types, a light transmitting type light valve device and a reflecting type light valve device, are known.
The light valve device generally comprises a semiconductor driving device and an optical function material such as liquid crystal or the like. To normally operate both constituents, a predetermined temperature (e.g., 60° C.) or lower must be maintained in the device. On the other hand, light from the light source, except for light that is to be finally projected, is absorbed by the light valve device and its peripheral optical elements and the like, and this light turns to heat. Accordingly, in a projection type video display device, the light valve device must be cooled so as not to overheat beyond a range of normal operation. The significance of cooling is becoming more and more important with an increase in the intensity of the light-source light for recent high-brightness projection video images, since the increase in the light-source light intensity increases the amount of heat generation which occurs in the light valve device.
Further, in such a display device, as the optical system brings the light of the image from the light valve device into focus, images of foreign particles, such as dust attached around the light valve device, are enlarged and projected on the screen or the like. Accordingly, prevention of dust around the light valve device is also an important problem to be solved.
Conventionally, a display device using a reflecting type light valve device is disclosed in Japanese Published Unexamined Patent Application No. Sho 64-5174. Further, a technique to cool the reflecting type light valve device in a display device is disclosed in Japanese Published Unexamined Patent Application No. Sho 62-294230. According to this technique, a cooling device is provided on the rear of a liquid crystal panel operating as the reflecting type light valve device.
Further, a technique to prevent dust in the display device is disclosed in Japanese Published Unexamined Patent Application, No. Hei 7-152009. According to this technique, a liquid crystal panel operating as a light transmitting type light valve device is placed within an enclosed space, and air within the enclosed space is circulated to radiate heat generated by the liquid crystal panel and transmit the heat to the outside of the enclosed space.
In the device disclosed in Japanese Published Unexamined Patent Application No. Sho 64-SI74, the cooling of the light valve device and dust prevention around the light valve device are not considered, and the disturbance of normal operation due to the above-described overheating and the occurrence of shadows on the screen due to dust have not been fully considered.
Further, in the technique disclosed in Japanese Published Unexamined Patent Application No. Sho 62-294230, the prevention of dust around the light valve device is not considered, and the occurrence of shadows on the screen due to dust has not been fully considered.
Further, in the technique disclosed in Japanese Published Unexamined Patent Application No. Hei 7-152009, since the cooling is performed via the air present within the enclosed space, efficient cooling cannot be expected. Further, in a case where the amount of heating increases due to an increase in the light-source light intensity, the light valve device might not be sufficiently cooled. In this case, the display device cannot be normally operated, and this problem has not been fully considered.
Accordingly, the present invention has an object to provide a projection type display device which efficiently performs dust prevention around the light valve device and cooling of a light valve device.